Electronic and structural properties of mixed-cation hybrid perovskites studied using an efficient spin-orbit included DFT-1/2 approach.

Fundamental understanding and optimization of the emerging mixed organic-inorganic hybrid perovskites for solar cells require multiscale modeling starting from ab initio quantum mechanics methods. Particularly, it is important to correctly predict the structural and electronic properties such as phase stability, lattice parameters, band gaps, and band structures. Although density functional theory is the method of choice to address these properties and generate the input for subsequent multiscale, high-throughput, and data-driven approaches, standard exchange correlation functionals fail to reproduce the bandgap, particularly if spin-orbit coupling (SOC) is correctly taken into account. While many SOC-included hybrid functionals suffer from low transferability between different molecular ions and are computationally costly, we propose an efficient multistep simulation protocol based on the DFT-1/2 method. We apply this approach to APbI3 with A: FA, MA, Cs, and systems with mixed cations and show how the choice of the A-cation modifies the Pb-I scaffold and the hydrogen bonding and discuss their interplay with structural stability. Furthermore, band gaps, band structures, Rashba band splitting, Born effective charges as well as partial density of states (PDOS) are compared for different cases w/wo the SOC effect and the DFT-1/2 approach.

Insight into the application of supercritical water oxidation for dichlorvos degradation: experimental and simulation aspects.

Dichlorvos or 2,2-dichlorovinyl dimethyl phosphate (DDVP) (C4H7Cl2O4P) is a chlorinated organophosphorus pesticide, which is frequently detected in agricultural wastewater. Herein, a batch reactor was used to carry out the supercritical water oxidation (SCWO) of a synthetic wastewater containing dichlorvos as a very hazardous agricultural pollutant. To do so, the impact of four operating parameters including dichlorvos concentration (100-500 ppm), oxidant coefficient (0.7-2), temperature (300-500°C) and time (0-100 s) on dichlorvos removal was optimized by the response surface method (RSM). According to the obtained results, at optimal conditions (i.e. initial concentration of dichlorvos 107.5 ppm, oxidation ratio 1.9234, temperature 419.9°C and time 79.94 s), as an index for dichlorvos removal, the chemical oxygen demand (COD) was found to be about 96.34%. Also, the results of high-performance liquid chromatography test showed that dichloroacetaldehyde (C2CL2H2O) and dichloroacetic acid (C2CL2H2O2) were created as intermediate substances during the dichlorvos degradation. Further, the molecular dynamics simulation was performed using ReaxFF force field to show the reaction path and products obtained in each step of the dichlorvos removal. Finally, as an indication, the simulation results indicated a good coordination with the experimental results.

Electronic and geometrical parametrization of the role of organic/inorganic cations on the photovoltaic perovskite band gap.

Recent state-of-the-art analysis techniques have revealed the high sensitivity of new generation perovskite photovoltaics to the organic/inorganic A-cation's chemical composition and atomic configuration. Various studies have focused on an extensive list of potential candidates to find the best A-cation with optimum stability and efficiency output. Regarding the perovskite band gap, different characteristics such as cation size, constituent elements, atomic configuration, possible bonding potential and induced lattice distortion, have been considered to screen plausible A-cations. However, there is not a comprehensive and comparative framework for developing predictive models because of the strong correlation between governing parameters. In this research, we develop an innovative approach, using first principle methods, to parametrize the role of A-cation on the regulation of the well-known ABX3 perovskites band gap in a quantitative and comparative form. Parameters are introduced concerning the A-cation impact on the shared electrons of the B-X bonds, whose s and p states control the whole band structure. The A-cation induced geometrical distortion on the BX3 network, including the subsequent bond length and bond angle, are designated as indirect parameters; and its impact on the electronic states of B-X bonding through long range electronic interactions, is attributed as the direct role. Dissociation of correlative parameters is achieved by comparing the electronic properties of the BX3 network including and excluding their A-cation, as well as swapping different A-cations on the corresponding equivalent BX3 scaffolds. The governing mechanisms behind the direct/indirect contribution of Cs, methylammonium (MA) and formamidinium (FA) cations, regarding their impact on electronic charge density distribution and bonding tendency via the introduced parametrization, are investigated and discussed.